Selection of sites for intramuscular injections in the neck of the horse.

The research examines the optimal areas for injecting substances into the neck muscles of horses to avoid depositing these substances on the surface of neck vertebrae, muscle sheaths, and certain ligaments. The best injection site was found to be the muscle mass over the fifth cervical vertebra.

Research Methodology

• The researchers carried out their study on several ponies and horses that were under profound anaesthesia prior to euthanasia. The primary focus was the cervical (neck) muscle where varying depths and levels were intramuscularly injected with a radio-opaque marker.
• After the injection, each animal’s neck was sectioned and radiographed, effectively allowing for a clear view of the injection’s impact, and where the material had been distributed.

Study Findings

• Results from the study highlighted the need for caution in deciding the injection site, as poor selection could lead to deposition of the injection material on the periosteal surface of the neck bones (cervical vertebrae), or on the ligamentum nuchae and fascial sheaths, tissues connecting and surrounding the muscles in the horse’s neck region.
• The study indicated that the muscle mass over the third cervical vertebra was notably less dense, but increased in the more caudal (closer to the rear) regions of the neck.
• From the data, the researchers concluded that the best spot for an intramuscular injection was at the level of the fifth cervical vertebra, just ventral (beneath or towards the belly side) to the funicular part of the ligamentum nuchae but dorsal (above or towards the back side) to the brachiocephalic muscle, a large muscle located on either side of the horse’s neck.
• Nonetheless, the study also noted that even at this optimal position, the injected material sometimes still infiltrated intermuscular fascial sheaths—thin layers of fibrous tissue enclosing a muscle or group of muscles.